Electrical discharge material and method of manufacturing it



Oct. 29, 1935. c. H. BRASELTON ELECTRICAL DISCHARGE MATERIAL AND METHOD OF MANUFACTURING IT Filed June 3, 1930 llllllllllllll I- I !!Iii!!niii w I VENTOR O0 4 ATTORNEY Patented Oct. 29, 1935 UNITED STATES ELECTRICAL DISCHARGE MATERIAL AND METHOD OF MANUFACTURING IT Chester H. Braselton, New York, N. Y., assignor to Sirian Lamp Company, Newark, N. J., a corporation of Delaware Application June 3, 1930, Serial No. 459,047

21 Claims.

This invention relates to electrical discharge material having a minimum of inert or detrimental residue, and also to its application as an electron emitting surface in an electrical discharge device.

One of the objects of the invention is to provide such an electrical discharge material having relatively uniform characteristics throughout and extending over its emitting surface and as free as possible from any inert or detrimental residue which has heretofore been due to binding materials.

The invention also relates to a method of applying such material to the surface of conducting material so that it will be combined therewith mechanically in as integral a manner as possible and will afford an intimate contact between the electron emitting material and the conducting material.

A specific application of the invention also relates to an electron device and its method of application thereto.

The invention also relates to the method of manufacturing the electrical discharge material or element and the method whereby it is applied to conducting materials and the products of such methods.

Other objects of the invention and objects relating to the specific uses of the electrical discharge material will be apparent as the description of the invention proceeds.

Several embodiments of the invention have been illustrated in the accompanying drawing in which:

Fig. l is a solid bar of the electron emitting material Fig. 2 is a perspective view of a wire coated with the electron emitting material;

Fig. 3 is a section through the wire shown in Fig. 2;

Fig. 4 is a perspective view of a metallic ribbon which is coated with the electron emitting material;

Fig. 5 is a section through the ribbon shown in Fig. 4;

Fig. 6 is a perspective view of a hollow metallic cylinder coated with the electron emitting material;

Fig. '7 is a section through the cylinder shown in Fig. 6; and

Fig. 8 is a perspective view of a thermionic amplifying tube incorporating the invention.

It is well known that certain materialsemit electrons more readily than others when heated in vacuo or in the presence of a gas. Such ma- 5 terials are the oxides of metals such as calcium, strontium, barium, and thorium, and many others well known in the art, as, for example, those of the rare earth group. The oxides of calcium, strontium, and barium emit at relatively low 10 temperatures so that these three or combinations of two or more of them are usually used for this purpose. However it is difiicult to make these oxides adhere to a filament or other surface desired to be made electron emitting and it has 15 usually been the practice to mix these oxides with an organic binder which can then be driven oil by heating when the materials have been applied to the surface. The results obtained by this method of applying the electron materials are not completely satisfactory because after the binder has been driven off the mechanical bond is weakened.

The present invention contemplates the mixing of compounds, with a binder which is soluble in 25 and which will chemically combine with the surrounding atmosphere under the influence of heat to form an electron emitting material and having particles of such minute size that they fill in the spaces between the particles of the 30 main portion of the electron emitting materials to bind these particles closely together and hold the whole mass securely upon the surface to which it is applied. During this action the binder and in some cases the compounds con- 5 taining the electron emitting materials are converted to the proper oxides and the whole mass becomes completely electron emitting all other inactive elements having been substantially driven oif. 40

I prefer to prepare the electron emitting material by mixing a carbonate of one of the metals mentioned above with a halogen of salt of one of those metals which has been dissolved in distilled water. Thus I may mix barium carbonate and strontium carbonate with sufficient barium chloride for a binder, add distilled water until a paste of the desired consistency is produced, and.

then grind the entire mixture until a very fine grain is obtained. The material may then be molded into any shape, as the cylindrical rod 50 emitting 20 I sleeve I6. 45'

illustrated at ID in Fig. 1, and dried. After the material has been dried I heat it in air to a temperature and for a suflicient time to con-. vert substantially all of the chloride to the monoxide with the liberation of the chlorine. At this stage there may be a slight amount of the chloride remaining which may be finally converted or discharged in an additional step to be hereinafter described. The equation involved is a substitution of oxygen for chlorine, thus:

The barium oxide thus formed is so finely divided that it acts as inter-grain cement, holding the particles of the material compactly together. I

It may be found desirable to speed up the above reaction in which the oxygen is substituted for the halogen element in the binder material by any convenient method as by heating in an atmosphere of oxygen, or adding to the mixture of materials before heating the nitrate of one of the metals whose oxide is electron emitting, such as barium nitrate, to the mixture of materials. The barium nitrate when heated will liberate nitric oxide which will readily combine with the barium chloride. The reactions involved are as follows:

BaNOs=BaO+NO2 BaCl+NO2=BaO+NO+Cl integral with the base so that it is mechanically well bonded. Figs. 2 and 3 show the coating H as applied to a filamentary wire I2. In Figs. 4 and 5 a coating 13 has been shown formed upon a ribbon I4 of metal and in Figs. 6 and '7 the coating I5 is shown upon a hollow cylindrical In all of these applications of the electron emitting material it maybe. applied in .a very uniform manner by mixing the material,

for example the barium and strontium carbonates and sufficient barium chloride for a binder in a thin paste, with water, as already described, and applying to the metal base in any desired manner such as by brushing or spraying upon the surface in consecutive layers, preferably drying the coating in each case before the next layer is applied. I have found that about four layers are sufficient to give an adequate coating and each layer may be heated to about 400 C. in air to partially carry out the first step of the process with the conversion of some of the chlorides to oxides and elimination of some chlorides before the next layer is applied. Then when the four layers have been applied in this manner the entire coated metal surface may be raised to a temperature around 600 C. to 700 C., but under the temperature of dissociation of the carbonate into the monoxides, to completely change all the chloride to the monoxide.

The coating thus appliedhas no organic binder, is very stable, and provides a dense structure intimately bonded to the base. The emission emciency of the coating is improved because it contains no inert material, all of the materials being active.

In one instance where it was desired to coat a wire with the material good results were obtained by mixing ten grams of barium carbonate with seven and one-half grams of strontium carbonate to which was added two grams of barium chloride. Enough distilled water was added to make a paste and the entire mixture was ground twenty hours to produce a very fine grain size. mixture was then applied to a filamentary wire which was maintained at a temperature of 90 C. which quickly dried the material. The temperature of the wire was then raised to about 400 C. which caused a part of the barium chlo- 10 ride to dissociate and form an oxide producing an oxychloride mixture but still retaining the carbonate. About four coatings of this material were applied to the filamentary wire which was again heated to a temperature of around 600 C. to 700? C. in the air for sufiicient time to substantially convert all of the chloride binder to the monoxide with the elimination oi. chlorine.

At this stage the material is well bonded to the base so that a wire coated with the material may be readily handled and wound upon a spool before it is used. If not used immediately the barium monoxide may be converted by the action of the air into the dioxide or hydroxide but it will always be in such a condition that it can be converted again into the monoxide by heating and it will maintain its binding effect on the rest of the material.

In Fig. 8 is illustrated one form of electron device in which the invention may be used. An evacuated envelope I! is provided with the usual inturned press I8, the whole mounted on a base (not shown) provided with terminals for making the outside connection. A tubular cathode I9 is secured at its lower end by a metal strap 20 which is welded to a support post 2| sealed in the press l8 and at its upper end by a strap 22 which is welded to a support 23 sealed in a glass bead 24 mounted transversely to the cathode l9 and inback of it. This cathode is similar to the coated cylinder I6 shown in Fig. 6 and is adapted to be raised to an electron emitting temperature by means of a heating filament 25 which is coated with insulating material and bent in the form 0d a hairpin and inserted in the lower end of the cathode with the two free ends: extending outwardly at the bottom. These ends are welded to short support rods 26 which are sealed in the press IS. A helical grid 21 is positioned around the cathode I9 and may be welded to a support rod 28 which is supported at. its lower end upon a rod 29 which is sealed in the press [8 and at its upper end by means of a short connecting rod 30 which is welded to an upright 3| sealed in the head 24. The anode 32 comprises two plates 65 each having a semi-cylindrical portion 33 provided with two diametrically extending side flanges 34 for securing the two sections together and strengthening the cylinder thus formed. A pair of support rods 35 mounted in the press I8 extend upwardly between the flanges 34 which may be provided with grooves to receive them and are bent backwardly over the top of the anode and downwardly again being sealed into the glass bead 24 thus anchoring both the top and bottom of the anode with respect to the other elements. The whole structure may be additionally supported by means of a rod 36 sealed in the press It! and bent backwardly and upwardly where it may be sealed into the bead 24.

Such an electron device may be used as an amplifier or detector, of electrical impulses or the grid may be omitted and the device used as a'rectifier of alternating current.

While an independently heated cathode adapt- This 5 ed preferably for use with alternating current has been shown a filamentary cathode may also be used either in the form of the wire shown in Fig. 2 or the coated ribbon shown in Fig. 4. The use of the electron emitter is not to be restricted however to amplifying devices as it may be used anywhere or under any condition Where an electron emission is desired.

When the material is placed in a device as described above the pressure of the atmosphere surrounding the material is reduced or an inert atmosphere is introduced into the device and the temperature then raised to in the neighborhood of 900 to 1200 C. for sufiicient time until the carbonates, if such are used, dissociate into monoxides, with the resultant mass constituting practically all monoxides and therefore being electron emitting under the influence of heat. The equation involved is as follows:

SrCOz +BaCOs=SrO +BaO +2CO2 It is to be noted that when the halogen element has been eliminated from the binder the material is in a stable form suitable for handling and that an additional heating is necessary to render it electron emitting. Where immediate use is contemplated however the completed electron emitting material may be produced at one heating by providing suitable conditions as, for example, an atmosphere of oxygen as the heating commences to convert the halogen compound binder to the monoxide and an atmosphere of inert gas or of greatly reduced pressure when the higher temperatures for dissociating the carbonates are attained.

While the material and process for forming it has been described specifically in connection with the carbonates and oxides of barium and strontium it is to be understood that the carbonate or oxide of any metal whose oxide will emit electrons may be used.

While the chlorides of the metals are specified as being preferable to produce the binding effect it has been found that the other halogen compounds such as fluorides, iodides, and bromides may be used.

A compound of any one of the metals men tioned may be used along with a halogen compound of it or of any of the others, or combinations may be resorted to as the combination of barium and strontium referred to above. This combination of barium and strontium has been found to be highly advantageous at relatively low temperatures as is also a combination of barium and calcium oxides. However other oxides may be used if high temperatures are desired and the invention contemplates the use of any of these materials in any desired combination.

What I claim is:

1. The method of making a material adapted to be subsequently converted into an electron emitting material which comprises mixing compounds of barium and strontium adapted to dissociate at relatively high temperatures into barium and strontium monoxides with a liquid halogen compound capable of displacing its halogen compound with oxygen when heated in an oxygen atmosphere to form an electron emitting compound, and heating said mixture in an oxygen atmosphere to a temperature of about 700 C.

2. The method of making an electron emitting material which comprises mixing a dissociable oxygen-containing compound of an electron emitting oxide with a chloride solution capable of displacing the chlorine element with oxygen when heated in air to form an electron emitting compound, and heating said mixture in air to convert said chloride and then at a higher temperature to convert said compound into an electron emitting material.

3. The method of making a material'adapted to be subsequently made electron emitting which comprises mixing finely divided barium carbonate and strontium carbonate with a binder of a halogen salt adapted to displace its halogen element with oxygen when heated in an oxygen atmosphere to form an electron emitting monoxide and raising the temperature of said mixture to between 600 and 700 C. in the presence of oxygen to cause said reaction to take place.

4. The method of making an element adapted to be subsequently converted into electron emitter which comprises mixing a finely divided compound which is convertible into an electron emitting material with a halogen salt of one of the metals whose monoxides is electron emitting, adding distilled water until a paste of the desired consistency is formed, spreading said paste upon a supporting member, and heating said member and paste to a temperature in the neighborhood of 700 C. but under the temperature at which said first mentioned compound is converted into an electron emitting compound.

5. The method of making an element which is subsequently convertible into an electron emitter which comprises mixing carbonates of barium and strontium, adapted to be dissociated into the monoxides, with alkali earth metal halogen salt, adding distilled water till a paste of the desired consistency is formed, spreading the paste so formed upon a supporting member, and heating the supporting member in the presence of oxygen until said halogen salt has been changed and then at a higher temperature to convert said carbonates into an electron emitting compound.

6. The method of making an element which is convertible into an electron emitter which comprises mixing carbonates of barium and strontium with barium chloride, adding distilled water until a paste of the desired consistency is formed, spreading said paste upon a supporting member, heating said member and paste in the presence of oxygen to change said barium chloride and then at a higher temperature to convert said carbonates to barium monoxide.

'7. The method of preparing an electron emitting material which comprises mixing compounds of barium and strontium adapted to dissociate at relatively high temperatures into barium and strontium monoxides with a solution of a compound of the halogen group adapted to replace its halogen element when heated in the presence of oxygen with oxygen to form an electron emitting oxide, heating said mixture in the presence of oxygen to a temperature sufficient to dissociate the halogen compound but insufiicient to dissociate the barium and strontium compounds and heating said mixture in an inert or vacuous atmosphere to a relativelyhigh temperature surficient to dissociate the barium and strontium compounds.

8. The method of preparing an electron emitting material which comprises mixing compounds of barium and strontium adapted to dissociate at relatively high temperatures into barium and strontium monoxides with a solution of a chloride adapted to replace its chlorine element with oxygen when heated in the presence of oxygen to form an electron emitting oxide, heating said mixture in the presence of oxygen to a temperand strontium compounds, and heating said mixture to a relatively high temperature suflicient to dissociate the barium and strontium compounds in an inert or vacuous atmosphere. 7

9. The method of preparing an electron emitting material which comprises mixing compounds of barium and strontium adapted to dissociate at relatively high temperatures into barium and strontium monoxides with a solution of a halogen compound adapted to replace its halogen element with oxygen when heated in the presence of oxygen to form an electron emitting oxide, heating said mixture in the presence of oxygen to a temperature in the neighborhood of 600 to 700 C., and heating said mixture subsequently in an inert or vacuous atmosphere to a temperature of in the neighborhood of 900 to 1200 C.

10. The method of rendering a surface electron emitting which comprises mixing a compound adapted to dissociate at relatively high temperatures into an electron emitting substance with a solution of a compound adapted to be converted when heated in an oxygen atmosphere into an electron emitting material, applying the mixture so formed to the surface to be coated, heating said surface and mixture in an oxygen atmosphere to change said second mentioned compound into an electron emitting material, and heating said surface and material in an inert or vacuous atmosphere to a relatively high temperature to dissociate said first mentioned compound. Y

11. The method of rendering a surface electron emitting which comprises mixing a compound adapted to dissociate at relatively high temper-' atures into an electron emitting substance with a solution of a compound adapted to be converted when heated in an oxygen atmosphere into an electron emitting material, applying the mixture so formed to the surface to be coated, heating said surface and mixture in an oxygen atmosphere to a temperature of in the neighborhood of 600 to 700 C. and heating said surface and mixture in an inert or vacuousatmosphere to in the neighborhood of 900 to 1200 C.

12. The method of rendering a surface electron emitting which comprises mixing a compound adapted to dissociate at relatively high temperatures into an electron emitting substance with a solution of a compound of the halogen group adapted to replace its halogen element with oxygen when heated inan oxygen atmosphere to form an electron emitting oxide, applying the mixture so formed to the surface to be coated,

. heating said surface and mixture in an oxygen atmosphere to change said halogen compound into an electron emitting compound, and heating to a relatively high temperature in an inert or vacuous atmosphere to dissociate said first mentioned compound.

13. The method of rendering a metallic surface electron emitting which comprises mixing compounds of barium and strontium adapted to dissociate at relatively high temperatures into barium and strontium moncxides with a solution of a compound of the halogen group adapted to replace its halogen element with oxygen when heated in an oxygen atmosphere to form an electron emitting oxide, applying the mixture so formed to the surface to be coated, heating said surface and mixture in an oxygen atmosphere to convert said halogen compound into an electron emittingcompound, and heating said surface and mixture in an inert or vacuous atmosphere to a relatively high temperature to dissociate said first mentioned compounds.

14. The method of rendering a metallic surface electron emitting which comprises mixing 5 carbonates'of barium and strontium with a solution of a chloride adapted to replace its chlorine element with oxygen when heated in an oxygen atmosphere to form an electron emitting oxide, applying the mixture so formed to the surface 10 to be coated, heating said surface and mixture in an oxygen atmosphere to in the neighborhood of 600 to 700 C., and heating said surface and mixture in an inert or vacuous atmosphere to a. temperature in the neighborhood of 900 to 15. 1200 c. I V 15. The method of rendering a surface electron emitting which comprises mixing calcium carbonate with a solution of barium chloride,

grinding said mixure into finely divided particles, 20".

applying the material thus formed to the surface, raising the temperature of said surface sufwhich comprises mixing compounds of barium 30- and strontium adapted to be dissociated into barium and strontium monoxideswith a halogen salt, adding distilled water until a paste of the desired consistency isformed, spreading the paste so formed upon a supporting member, and heating 35' the supporting member in an oxygen atmosphere until said halogen salt has been changed to an electron emitting compound but under the .temperature of dissociation of said barium and strontium compounds.

17. The method of preparing an electron emitting material comprising mixlng a compound containing calcium adapted to dissociate at a relatively high temperature into an electron emitting substance with an alkali earth metal halogen 45 compound adapted to react when heated in air to form an electron emitting material, heating said mixture in air below the dissociation temperature of said first mentioned compound sufficient to dissociate the halogen compound, and heating said mixture further to a relatively high temperature sufficient to dissociate the barium and strontium compounds.

18. The method of rendering a surface electron emitting which comprises mixing a compound containing calcium and adapted to dissociate at relatively high temperatures into an electron emitting substance, with an alkali earth metal halogen compoundadapted to be converted when heated in an oxygen atmosphere into an electron emitting material, applying the mixture so formed to the surface to be coated, heating said surface and mixture in an oxygen atmosphere to change the second mentioned compound to an electron emitting material, and heating said surface and material in an inert or vacuous atmosphere to a relatively high temperature to dissociate said first mentioned compound.

'19. A process of forming an electron emitting 'material which comprises forming an intimate vacuous atmosphere to also decompose the carbonate to said oxide, the oxide formed from the chloride serving as a binder during the second heating operation.

20. A process of forming an electron emitting material which comprises forming an intimate mixture of a chloride and a carbonate of one or more alkali earth metals, heating in the presence of air to decompose the chloride into the oxide,

0 and then heating at a more elevated temperature of these compounds.

to decompose the carbonate into the oxide, the oxide formed from the chloride serving as a binder during the second heating operation.

21. A process of forming an electron emitting material which comprises forming an intimate mixture of a chloride, a nitrate and a carbonate of one or more alkali earth metals and heating this mixture to form the metal oxides from each CHESTER H. BRASELTON. 

